Adaptive optics is utilized to modify optical wavefronts. As an example, adaptive optics may be used to correct for existing aberrations recognized by optical systems. Specifically, adaptive optics may be used to correct aberrant wavefronts by modifying shape of the wavefront. Such correction appeals to many fields, including, but not limited to, astronomy, ophthalmology, and microscopy. As an example, in the field of astronomy adaptive optics may compensate for aberrations due to atmospheric turbulence and/or telescopic errors (i.e., lens errors). As a further example, in the field of ophthalmology, adaptive optics provide a means of measuring and compensating for aberrations in human vision. In addition, adaptive optics may be utilized to modify optical wavefronts without consideration of aberrations. It should be noted herein that a wavefront can be defined as a plurality of locations in space having a constant phase.
It should be noted that the term “optical phase” refers to the difference between the place or time where the sinusoidal amplitude of the electromagnetic field that is a light wave is at peak, and the place or time at which it is reduced, simply because it is a sine wave. E=A sin(2πft+phase). Since light extends in three dimensions, we call a surface of constant phase a wavefront. It is the shape of this surface that the deformable mirror will change, and we describe that as a change in the local phase, but the term should be understood to mean a change in the local shape of this surface of constant phase.
Adaptive optics attempt to correct for existing aberrations via use of wavefront sensors, controllers, and/or wavefront corrective devices. FIG. 1 is a schematic diagram illustrating an example of a basic adaptive-optical wavefront modification system 10 that contains a wavefront sensor 20, a controller 30, a wavefront corrective device 40, such as a deformable mirror 40, and a beam splitter 50. As is known by those having ordinary skill in the art, the wavefront sensor 20 assesses, or measures, aberrations in an aberrant wavefront received by the adaptive-optical wavefront modification system 10. An example of a wavefront sensor 20 is a Shack-Hartmann sensor, such as a WaveScope wavefront measurement system manufactured by Adaptive Optics Associates of Massachusetts, USA.
Typically, a wavefront sensor 20 uses software to assess changes in wavefront shape caused by the deformable mirror 40, after energizing by the controller 30, as explained below. As an example, information regarding wavefront shape changing may be used by the wavefront sensor 20 to create a conjugate shape on the deformable mirror 40 to correct wavefront aberrations. The wavefront sensor 20 may use a least-squares estimation of the wavefront to determine the changes in the deformable mirror 40 caused by energizing.
The beam splitter 50 is used by the basic adaptive-optical wavefront modification system 10 to separate a part of the corrected wavefront. Since one having ordinary skill in the art would understand how such separation is performed, a detailed description of separation performed by the beam splitter 50 is not provided herein.
After assessing aberrations, the wavefront sensor 20 transmits information to the controller 30 regarding requirements to create the conjugate shape on the deformable mirror 40, as signified by the dotted line located between the wavefront sensor 20 and the controller 30. In accordance with requirements to provide the conjugate shape, the controller 30 transmits control signals, such as, but not limited to, a voltage, to the deformable mirror 40. The received voltage causes actuators (not shown) located within the deformable mirror 40 to move in a surface normal direction in accordance with stroke of each actuator and the control signals, thereby providing a small local step within the deformable mirror 40, or deforming the deformable mirror 40. For simplicity, in the remainder of this document the deformation of the deformable mirror or wavefront correcting device will be described as a step, though in practice this deformation may not be step-like: it might be smooth, ramped, or arbitrarily shaped. The step of the deformable mirror 40 modifies the wavefront so as to impress on the wavefront a change of shape in the areas of the wavefront that have been reflected by the step of the deformable mirror 40.
The step, through the change of phase in the wavefront, corrects aberrations in the received aberrant wavefront by canceling aberrations with the conjugate shape provided. Specifically, the conjugate shape provided to the aberrant wavefront is intended to cancel the aberrations. Since one having ordinary skill in the art would understand how the actuators are caused to move, a detailed description of actuator movement is not provided herein. It should be noted that in the present disclosure, the term actuator is utilized to identify elements of a deformable mirror that have a stroke.
More commonly known deformable mirrors have actuators that are either piezoelectric or electrostatic devices. Unfortunately, known deformable mirrors are characterized as being difficult to achieve more than a few microns of actuator stroke without greatly increasing expense and/or complexity of the deformable mirror. In addition, it is a general rule that the larger the actuator stroke of a deformable mirror, the more that aberrations in an aberrant wavefront may be removed. Therefore, aberrant wavefront correction by current adaptive-optical wavefront modification systems is restricted. In addition, the amount of altering of the shape of a wavefront is restricted.
Thus, a heretofore unaddressed need exists in the industry to address the aforementioned deficiencies and inadequacies.